To maximize cooling efficiency in conditioning an aircraft cabin for example, it is known to recirculate some cabin air and to mix the warm cabin air with cooler air cooled by the environmental control system. An air motive source is provided for recirculating the cabin air which is at a lower pressure than the cooler air cooled by the environmental control system. In typical prior proposals, the warmer low pressure cabin air and cooler, higher-pressure air are introduced to a mixing device, from where the mixed air is reintroduced to the cabin. Such environmental control systems may be used to condition the environment in other aircraft and generally in other vehicle compartments.
Jet pump apparatus are known for mixing higher and lower pressure gases in order to provide a mixed gas supply to a downstream apparatus. Jet pumps may alternatively be called injectors, airmovers, inducers, inspirators, vacuum pumps, ejectors, pressure exchangers, venturis, etc. These include a mixing chamber to which higher and lower pressure gas supplies are provided.
It has been found that in a conventional jet pump design, there is preferred relationship between the mixing chamber cross section and mixing chamber length for optimum mixing, this relationship commonly being expressed where the mixing chamber is of circular cross section, as a ratio between the mixing chamber length and diameter, which typically is about 8. Achieving this ratio places constraints on jet pump design. Particularly, in some applications there is insufficient space to accommodate a jet pump with a sufficiently long mixing chamber.